This recent response -- (At BU, some professors will raise or lower your final grade based on your class participation and performance. Neither occurs often but having your grade lowered will really only occur if you are obviously not prepared for class.) -- reflects the policy at Roger Williams University School of Law as well. Check the syllabus for each class, though. Usually, faculty members are allowed to adjust the grades somewhat, according to the rules and regulations adopted by a committee of their peers -- some will employ a more conservative approach in their own class however.
Of course, the best advice to a student is this: show up prepared and participate as much as you can. Why? In so doing, you are "practicing" law, and -- through trial and error (falling off the horse and getting back on) -- getting better and better at what you are expected to learn in law school, that is, thinking like a lawyer, and speaking the "language of the law" fluently.